Canine Hip Dysplasia

Malformation of the hip joint, or hip dysplasia, is a serious medical problem. The condition is observed in humans (especially in young females), gorillas, cattle, chickens, bears and cats. But, hip dysplasia is most prevalent among dogs.

What is Canine hip dysplasia? 

Hip dysplasia is a developmental abnormality of the hip joint. Disconformity of the femoral head in relation to the acetabulum allows excessive movement of the femoral head leading to damage, inflammation and eventually weakening of the joint. The amount of synovial fluid is increased and the round ligament which binds the femoral head to the acetabulum becomes swollen and stretched. The normally smooth cartilage covering the ends of the opposing bones is abraded and the joint capsule is inflamed and thickened. Muscles in the region of the hip joint are weakened and diminished in bulk. As the disease advances, the bones are damaged.

Recent evidence indicates that the hip is not the only joint affected in dysplastic dogs. The shoulder and knee joints, and the joints between individual vertebra that make up the backbone often show similar changes. Males and females are affected with about equal frequency.

Hip dysplasia is not obvious in very young dogs. The joints of newborn pups appear disease-free and do not show abnormal changes. There is no relationship between hip dysplasia and the degree of inclination of the femoral head with reference to the shaft of the femur or the degree of femoral head rotation (anteversion).

Hip dysplasia is common in the large breeds, such as St. Bernards, German Shepherd Dogs, Golden Retrievers, English Bulldogs, Collies, Doberman Pinschers, Boxers, Alaskan Malamutes, Old English Sheepdogs, Huskies, Setters, Pointers, and Standard Poodles. While the smaller breeds are not spared, hip dysplasia occurs less often in those breeds than in larger dogs.

What are the signs for hip dysplasia? 

Decreased activity with varying degrees of arthritis and joint pain are early manifestation. These signs are often first observed between the ages of four months and one year. Young dogs may have a swaying and unsteady gait. Their hind legs may be drawn forward with more weight than usual being placed on the forelimbs. Afflicted dogs often run with both hind legs moving together, a gait that has been described as "bunny hopping." As the disease progresses, the animal may have difficulty rising from a sitting or lying position. Stairs are difficult to climb and the dog may whimper or snap when the affected hip joint is manipulated. The disease is progressive and often crippling. Pain limits movement of the joint. Some dogs experience little discomfort despite abnormal changes in the joints, however. Running and intense activity aggravate the condition and can reveal signs of disease in an otherwise sound animal.  

 Diagnosis. 

Although observation can arouse suspicion of hip dysplasia, the diagnosis can only be established by x-ray examination. The examination requires general anesthesia or deep sedation. The animal is placed on its back. The legs are then extended together to their maximum position and the stifles are rotated inward. Radiographs taken in that position reveal changes which cannot be detected without proper positioning.

In the normal joint, the head of the femur fits congruently into the acetabulum. The center of the femoral head is located well within the rim of the acetabulum. Normal joints are scored as excellent,good or fair, depending on the shape and relationship of the opposing bones. In the dysplastic joint the femoral head conforms poorly to the acetabulum. More space is evident between the opposing bones. Displacement of the femoral head is the hallmark of hip dysplasia. Subluxation is positive if the dorsal area of the acetabulum covers less than 50% of the femoral head. When the center of the femoral head is directly below the acetabular rim the severity of hip dysplasia is moderate; if displaced further it is severe. In advanced cases the acetabulum appears shallow and osteophytes are evident. The changes are often subtle and can be detected only by an experienced radiologist.

The term indeterminate is used when the diagnosis is in doubt. This is often the case in young dogs. It may be necessary to repeat the x-ray examination when the dogs are older. Changes characteristic of hip dysplasia may not be detected until animals are two years old.

Is hip dysplasia an hereditary disease? 

Hip dysplasia has an hereditary basis. The pattern of inheritance suggests that more than one gene is involved; however, the number is unknown. The practical implication is that breeding dogs for desirable traits, such as good temperament or large size may result in unwitting selection of animals that are susceptible to hip dysplasia. When both parents have hip dysplasia a high percentage of the offspring also become dysplastic. Selectively breeding animals that are disease-free by radiographic criteria reduces the occurrence of disease to 30%. Further reduction can be achieved by breeding dogs based on family performance and progeny testing.

It has long been the goal of dog fanciers to eradicate hip dysplasia. Selective breeding has led to some improvements, but the disease has not been eliminated. A major problem is that we do not know the cause of hip dysplasia and we have only a few hints about factors that favor the expression of disease. A dog with normal hips may have one or more characteristics that promote the development of hip dysplasia only when they occur in combination with other predisposing factors, Thus two parents with disease-free hips may have dysplastic offspring.

Another concern relates to the accuracy of the radiographic method of diagnosing hip dysplasia. A more reliable diagnostic procedure is needed to identify adult dogs with subtle joint abnormalities that presently cannot be detected by x-ray examination. It has been estimated that up to 25% of the dogs that have "normal" hips as judged by a radiograph actually have joint disease.

Can the disease be prevented? 

Hip dysplasia cannot be prevented, but its severity can be lessened. The time of appearance and the rate of progression of hip dysplasia are influenced by the growth rate of dogs. The reason is unknown; however, the rate at which tissues develop in the region of the hip joint seems to be important. Studies have shown that slowing puppy growth during the first three months of life delays the appearance of hip dysplasia and reduces its severity. While the observation is encouraging, it must be substantiated and thoroughly explored. For instance, we need to define a diet which not only provides the necessary requirements for growing dogs but also moderates the development and severity of hip dysplasia. 

What is the treatment? 

Practical measures can give comfort to dysplastic animals. Mild exercise such as walking, swimming , or slow running is beneficial, but excessive activity such as jumping and prolonged running should be avoided. Warm packs and buffered aspirin can relieve the pain. However, aspirin and other medications do not arrest the destructive changes in the joint. (Dietary supplements have no effects.)